1. Field of the Invention
This invention relates to a method and apparatus for processing and propagating television camera signals for recording IP video signal over a network in a close circuit television system.
2. Description of the Prior Art
In a monitoring television system used, as one of information transmission system, at least one video cassette recorder or a digital video recorder is connected through an electronic switch to a plurality of television cameras and transmission lines. The electronic switch known as multiplexer or frame switcher provides for fast rate sequential switching for recording onto the video recorder a picture image of one camera after another.
In such an information transmission system, it is preferable to mutually lock the internal synchronizing signals of a plurality of television cameras and the electronic switching time to an external synchronizing signal, in order to prevent the recording from being disturbed during and immediately after the switching operation from one television camera to another. Such external synchronizing also provides for switching at a rate of 30 frames or 60 fields per second of, for example, the NTSC television system, and which is known as the real time rate.
A known apparatus for synchronizing a plurality of television cameras is an apparatus for transmitting an external synchronizing signals from an external synchronizing generator to the television cameras by injecting the external synchronizing signal into the video signal transmission line and locking an internal synchronizing signal generator of the television camera by means of the transmitted external synchronizing signal. Such an apparatus is disclosed in U.S. Pat. No. 4,603,352 the contents of which are incorporated herein by reference.
Another known apparatus for synchronizing the plurality of the television camera signals is an apparatus for memorizing each of the television camera signal in a memory circuit and feeding the signals to the video recorder, synchronously via the electronic switch from the memory circuits. Such an apparatus is disclosed in U.S. Pat. No. 5,267,039 the content of which are incorporated herein by reference.
Furthermore, the known apparatuses for recording plurality of camera signals at fast sequencing rate require that each individual camera signal will incorporate a coded identification signals, providing for simple retrieval of the signal through a coded selection. In the case of using analogue video cassette recorder, the coded identification is known to be recorded during the vertical blanking period of the television signals, but in the case of using a digital video recorder it is known that digital video recorders ignore the vertical blanking period and instead they employ a complex control software for indexing the files of the recorded digital signals of each individual camera.
Because the software programs for controlling the individual files of the digitally recorded camera signals are complex, it renders the processing, transferring and/or retrieval of the recorded digital signals to and from disks, tapes or other medium time consuming. Moreover, because of the limited capacity of the digital recorder's storage medium the digital video recorders record in a continuous FIFO (First In First Out) rotation, and it is necessary to introduce a protection software programs for the recorded alarms or event files in order to retain such recording for extended periods by excluding such alarms and events files from the FIFO process. The continued randomly changing, deletion and/or addition of protected files cause an inefficient FIFO recording in rotation, particularly when large numbers of television cameras are used. Moreover, the complexity of the software programs makes it impractical to combine plurality of digital recorders for increasing the overall storage capacity as needed or at will.
Large capacity digital recording systems such as network recorders with RAID storage (Redundant Array of Independent Disks), having large number of HDDs (Hard Disk Drive) that can be increased at will do provide for very large storage capacity needed in security system. However such network recorders must be fed with digital video signals in packets that include IP (Internet Protocol) addresses, as used in Ethernet network or the Internet, with each individual video signal source generating its own assigned or allotted IP or MAC address (Media Access Control address) as the source address. This restricts the use to only IP cameras or to analog cameras that are connected to IP video encoders or servers. Such multiple independent IP cameras and/or IP video servers cannot be individually programmed to sequence in concert with the other cameras or to timely generate their signals to the network recorder in a repeated accurate sequence. To create such organized, orderly IP serial video signal mandates a complex software program for enabling the network recorder to feed in sequence rotation a command to each IP camera or IP video server for initiating the transmission of each individual camera signal. Such recording network occupied with sequence commands from the recorder to the cameras limits the transmission rate from the cameras to the recorder and calls for very complex management software program which is expensive and difficult to handle.